Doping method

ABSTRACT

A first dose of first dopants is introduced into a semiconductor body having a first surface. A thickness of the semiconductor body is increased by forming a first semiconductor layer on the first surface of the semiconductor body. While forming the first semiconductor layer a final dose of doping in the first semiconductor layer is predominantly set by introducing at least 20% of the first dopants from the semiconductor body into the first semiconductor layer.

This application claims the benefit of German Application No.102017121693.6, filed on Sep. 19, 2017, which application is herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to a method of manufacturingsemiconductor devices and more specifically to a doping method of asemiconductor body.

BACKGROUND

Vertical power semiconductor devices that control a load current flowbetween a first load electrode at a front side and a second loadelectrode at a rear side of a semiconductor die typically include dopedregions that are formed in semiconductor layers, e.g., drift zones,compensation structures, buffer layers and/or field stop layers.

Properties of vertical dopant profiles of such doped regions, forexample, steepness, uniformity, smoothness and undulation may havesubstantial impact on device parameters. Typically, a vertical dopantprofile in an epitaxial layer is shaped by controlling a doping gassupply with time or by ion implantation followed by a heat treatment fordiffusing the implanted dopants.

There is a need for an improved doping method and for semiconductordevices with improved dopant profiles.

SUMMARY

The present disclosure relates to a method of manufacturingsemiconductor devices. The method includes i) introducing a first doseof first dopants into a semiconductor body having a first surface, ii)increasing a thickness of the semiconductor by forming a firstsemiconductor layer on the first surface of the semiconductor body.While forming the first semiconductor layer, a final dose of doping inthe first semiconductor layer is set by introducing at least 20% of thefirst dopants from the semiconductor body into at least a part of thefirst semiconductor layer.

Further embodiments are described in the dependent claims. Those skilledin the art will recognize additional features and advantages uponreading the following detailed description and on viewing theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present embodiments and are incorporated in andconstitute a part of this specification. The drawings illustrate thepresent embodiments and together with the description serve to explainprinciples of the embodiments. Further embodiments and intendedadvantages will be readily appreciated as they become better understoodby reference to the following detailed description.

FIG. 1 is a simplified flow-chart for illustrating a doping method;

FIG. 2A is a schematic graph illustrating a vertical dopant profileaccording to a simulation of effects of auto-doping for discussingbackground of the embodiments;

FIG. 2B is a schematic graph illustrating the effects of solid-statediffusion and auto-doping on a vertical dopant profile for discussingbackground of the embodiments;

FIG. 3A is a schematic vertical cross-sectional view of a semiconductorbody for illustrating a doping method using auto-doping according to anembodiment;

FIG. 3B is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 3A, after introducing first dopants in asurface portion;

FIG. 3C is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 3B, after increasing a thickness of thesemiconductor body;

FIG. 3D is a schematic graph illustrating a vertical dopant profile ofthe semiconductor body of FIG. 3C along line I-I′;

FIG. 4A is a schematic cross-sectional view of a deposition chamber forillustrating a doping method according to an embodiment concerningepitaxial growth without doping gas supply;

FIG. 4B is a schematic vertical cross-sectional view of the depositionchamber of FIG. 4A with a doping gas supply turned off;

FIG. 5A is a schematic vertical cross-sectional view of a portion of asemiconductor body for illustrating a doping method according to anembodiment defining a dopant dose by ion implantation, during ionimplantation of dopants into the semiconductor body;

FIG. 5B is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 5A, after a heat treatment;

FIG. 5C is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 5B, after increasing the thickness of thesemiconductor body by epitaxy;

FIG. 5D is a schematic graph illustrating vertical dopant profiles ofthe semiconductor bodies of FIGS. 5A to 5C;

FIG. 6A is a schematic vertical cross-sectional view of a portion of asemiconductor body for illustrating a doping method according to anembodiment defining a dopant dose by epitaxial growth, after forming anauxiliary layer by epitaxy;

FIG. 6B is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 6A, after increasing the thickness of thesemiconductor body by epitaxy;

FIG. 6C is a schematic graph illustrating vertical dopant profiles ofthe semiconductor bodies of FIGS. 6A and 6B;

FIG. 7A is a schematic vertical cross-sectional view of a portion of asemiconductor body for illustrating a method of manufacturing asemiconductor device with a field stop layer defined by auto-doping,after forming the field stop layer in a first epitaxial process;

FIG. 7B is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 7A, after forming a drift layer on the fieldstop layer;

FIG. 7C is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 7B, after forming transistor cells in thedrift layer;

FIG. 7D is a schematic graph illustrating a vertical dopant profile ofthe semiconductor body of FIG. 7C;

FIG. 8A is a schematic vertical cross-sectional view of a portion of asemiconductor body for illustrating a doping method for forming asuperjunction structure, after forming a surface portion containingfirst and second dopants of complementary conductivity type;

FIG. 8B is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 8A, after forming trenches in an epitaxiallayer formed on the surface portion, wherein a dopant distribution inthe epitaxial layer results to a high degree from auto-doping;

FIG. 8C is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 8B, after filling the trenches withsemiconductor material;

FIG. 8D is a schematic graph illustrating lateral dopant profiles of theportions of the semiconductor bodies of FIGS. 8B and 8C;

FIG. 9A is a schematic vertical cross-sectional view of a portion of asemiconductor body for illustrating a doping method according to anembodiment concerning a patterned surface portion, after forming thepatterned surface portion;

FIG. 9B is a schematic vertical cross-sectional view of thesemiconductor body of FIG. 9A, after increasing the thickness of thesemiconductor body by epitaxy;

FIG. 9C is a schematic graph illustrating a lateral dopant profile ofthe semiconductor body of FIG. 9B along line I-I; and

FIG. 10 is a schematic graph illustrating a vertical dopant profilepivotally obtained by auto-doping according to a further embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof and in which are shownby way of illustrations specific embodiments in which the embodimentsmay be practiced. It is to be understood that other embodiments may beutilized and structural or logical changes may be made without departingfrom the scope of the present disclosure. For example, featuresillustrated or described for one embodiment can be used on or inconjunction with other embodiments to yield yet a further embodiment. Itis intended that the present disclosure includes such modifications andvariations. The examples are described using specific language, whichshould not be construed as limiting the scope of the appending claims.The drawings are not scaled and are for illustrative purposes only.Corresponding elements are designated by the same reference signs in thedifferent drawings if not stated otherwise.

The terms “having”, “containing”, “including”, “comprising” and the likeare open, and the terms indicate the presence of stated structures,elements or features but do not preclude additional elements orfeatures. The articles “a”, “an” and “the” are intended to include theplural as well as the singular, unless the context clearly indicatesotherwise.

FIG. 1 is a schematic flow-chart for illustrating a doping method 1000.It will be appreciated that while doping method 1000 is illustrated anddescribed below as a series of steps or events, the illustrated orderingof such steps or events is not to be interpreted in a limiting sense.For example, the steps may occur concurrently with other steps or eventsapart from those illustrated and/or described herein. In addition, notall steps may be required to implement one or more aspects ofembodiments of the disclosure herein. Also, one or more of the stepsdepicted herein may be divided in one or more separate sub-steps and/orphases.

Referring to FIG. 1, process feature S100 includes introducing a firstdose of first dopants into a semiconductor body having a first surface.The semiconductor body may be a of a single-crystalline semiconductormaterial such as a silicon (Si) wafer, a germanium (Ge) wafer, a siliconcarbide (SiC) wafer or a wafer of a compound semiconductor, e.g.,gallium nitride (GaN) or gallium arsenide (GaAs). The first dopants maybe any impurity element that alters the electrical properties of thesemiconductor body. For example, in case the semiconductor body is basedon silicon, the first dopants may include boron (B), phosphorus (P),arsenic (As), antimony (Sb) sulfur (S) or selenium (Se) atoms, by way ofexample. For example, in case the semiconductor body is based on siliconcarbide, the first dopants may include nitrogen (N) and phosphorus (P)for n-type doping, by way of example.

The first dopants may be introduced through a first surface of thesemiconductor body by ion implantation, by way of example. A surfaceportion, in which the first dopants dominate exceed dopants alreadycontained in the semiconductor body, may be a blanket layer extending atuniform thickness along the first surface or may be a patterned layerselectively formed along first portions of the first surface and absentalong second portions of the first surface.

Process feature S200 increases the thickness of the semiconductor bodyby forming a first semiconductor layer, for example a Si or SiC layer onthe original first surface of the semiconductor body. During formationof the first semiconductor layer a final dopant dose and doping profilein the first semiconductor layer is set by transferring at least 20%, orat least 30%, or at least 50% or at least 70% of the first dopants fromthe surface portion of the semiconductor body into the firstsemiconductor layer. In other words, at least 20% of the first dopantspresent in the surface of the semiconductor body before formation of thefirst semiconductor layer migrate into the first semiconductor layer.

The first dopants may reach the first semiconductor layer by bothsolid-state diffusion and auto-doping. Solid-state diffusion results ina direct transition of dopant atoms from the surface portion into thefirst semiconductor layer. By contrast, for auto-doping the surfaceportion releases dopants into the ambient atmosphere through evaporationand the growing semiconductor layer reincorporates the released dopants.If the growth velocity of the semiconductor layer substantially exceedsthe direct solid-state diffusion of dopants from the surface portioninto the semiconductor layer, a portion of the resulting dopant profilein the semiconductor layer at a distance to the surface portion isdominated by dopants re-introduced after evaporation from thesemiconductor body.

Since dopant evaporation from the semiconductor body is supplied fromthe surface portion by solid-state diffusion, the total number ofevaporated dopants for auto-doping steadily decreases with increasingthickness of the semiconductor layer.

Auto-doping may be combined with intentional doping, wherein a gaseousdopant source containing a compound including the dopant atom is addedto a gaseous semiconductor source that contains atoms of thesemiconductor material. For example, up to 50% of the total dopant dosein the semiconductor layer may originate from an added dopant source.According to an embodiment, the supply of the gaseous dopant source intothe deposition chamber may be completely turned off during formation ofthe semiconductor layer such that a total dose of dopants in thesemiconductor layer as well as the vertical dopant profile areexclusively set by auto-doping and solid-state diffusion. The degree ofauto-doping depends also on the epitaxy tool, wherein on batch tools theeffect of auto-doping is more pronounced than in single wafer epitaxytools.

Compared to other doping methods for epitaxially grown semiconductorlayers, the doping method 1000 produces vertical doping profiles withcomparatively smooth gradients or even with several smooth gradientsthat extend over a comparatively large vertical distance of at least 5μm at high reproducibility, high homogeneity and precise total dopantdose across the semiconductor layer and the remaining diffused surfaceportion below the semiconductor layer at comparatively low effort.Several smooth gradients can be achieved for example by using differentdoping atoms with different diffusion coefficients like e.g. phosphorusand arsenic and/or antimony. For example, a dopant concentration in theepitaxially grown semiconductor layer may fall by two orders ofmagnitude across at least 3 μm or 5 μm or even 10 μm. At high dopingconcentration the doping profile can be steeper compared with lowdoping.

For example, conventional in-situ doping defines a vertical dopantprofile in an epitaxial layer by varying the supply of a gaseous dopantsource with time. But typically in-situ doping results in variations ofthe total dopant dose in the epitaxial layer. In additionreproducibility, smoothness and homogeneity of specific dopant profilesmay be unsatisfactory. In general, in-situ doping of epitaxial layersresults in comparatively large fluctuations of the total dopant dose andachieving well defined vertical dopant profiles at small tolerances is acomplex task, for example for low doping concentrations.

When shaping, on the other hand, vertical dopant profiles by ionimplants followed by a subsequent heat treatment, even comparativelyhigh thermal budgets result in only small diffusion depths.

By contrast, the doping method woo uses auto-doping in order to providereproducible results and homogeneously smooth profiles at no or only lowadditional thermal budget.

According to an embodiment, the first dose of first dopants isintroduced by ion implantation. Ion implants can supply a very preciseamount of dopants such that the total dopant dose contained in the firstsemiconductor layer and the diffused surface portion below the firstsemiconductor layer are precisely defined. The same holds for suchdevice parameters that are linked to the total dopant dose in the firstsemiconductor layer and the diffused surface portion. Ion implants atlow acceleration energies for the ions achieve high dopantconcentrations close to the first surface such that the effect ofauto-doping on the dopant profile in the first semiconductor layerprevails the effect of solid state diffusion to a higher degree. Forexample, the acceleration energy of phosphorus ions used as the firstdopants may be less than 150 keV or less than 100 keV or even less than50 keV.

According to an embodiment introduction of the first dose of firstdopants may include a sequence of several implants at different ionimplantation energies and/or implant angles. For example, at least oneion implantation may be performed at an implant angle at whichchanneling occurs. According to a further embodiment, a heat treatmentmay diffuse the implanted dopants prior to the formation of the firstsemiconductor layer to modulate the vertical dopant profile in thesurface portion of the semiconductor body before formation of the firstsemiconductor layer. Since the auto-doping profile in the firstsemiconductor layer depends on the vertical distribution of the firstdopants in the surface portion, a modulation of the vertical dopantprofile in the surface portion leads to a modulation of the verticaldopant profile in the first semiconductor layer. Shaping the dopingprofile in the surface portion by several implants and/or heattreatments adds further degrees of freedom for shaping the verticaltarget doping profile in the first semiconductor layer.

According to another embodiment, introducing the first dose of firstdopants may include in-diffusion from the gaseous phase. According to afurther embodiment, a surface portion forming a blanket layer may be anin-situ doped epitaxial layer formed prior to the formation of the firstsemiconductor layer. Also highly doped oxides, e.g. TEOS(tetraethylorthosilane) may be deposited at low temperatures on thefirst surface and/or in trenches extending from the first surface intothe semiconductor body and a high temperature heat treatment may diffusethe first dopants from the deposited oxide into the semiconductor body.

According to another embodiment at least two different types of dopantatoms are introduced into the semiconductor body, e.g. phosphorus atomsand arsenic atoms, and/or antimony atoms.

According to another embodiment an additional thin doped layer may bedeposited on the semiconductor body, e.g., by epitaxy, wherein the firstdopants are introduced into the additional thin in-situ doped layer. Thedopants may be introduced by in-situ doping, ion implantation ordiffusion from a diffusion source, for example. A thickness of the thindoped layer may range from 0.1 μm to 5 μm.

A thickness of the first semiconductor layer may be in a range from 5 μmto 35 μm. A semiconductor layer with a thickness in the range from 5 μmto 35 μm may form, e.g., a field stop layer. Field stop layers withsmooth and well-defined vertical dopant profiles allow to improve atleast one of softness during turn-off, short-circuit ruggedness andruggedness against cosmic radiation events.

A second semiconductor layer may be formed by epitaxy on the firstsemiconductor layer, wherein an average doping concentration in thesecond semiconductor layer is lower than a minimum dopant concentrationin the first semiconductor layer.

According to another embodiment, a first semiconductor layer with athickness in a range from 2 μm to 200 μm or with a thickness in a rangefrom 40 to 100 μm may provide the basis for a drift zone that includes asuperjunction structure. For example, in addition to the first dose offirst dopants a second dose of second dopants may be introduced into thesemiconductor body through the first surface, wherein the second dopantshave a conductivity type complementary to the conductivity type of thefirst dopants and wherein the first and the second dopants havedifferent diffusion constants for solid-state diffusion. By implementingtrench structures which will be filled with e.g. the same semiconductormaterial with e.g. low doping level the resulting different lateraloutdiffusion during a subsequent high-temperature treatment results in aseparation of the different doping atoms (like e.g. boron and arsenicatoms), so that a superjunction structure will be formed in that way.

According to an embodiment, the first dopants include phosphorus atomsand the first semiconductor layer is formed in a deposition chamber at adeposition temperature above 1100° C., at a pressure below 30 Torr (4kPa) and at a H₂ flow rate lower than 30 slm, wherein a deposition rateof at least 1 μm/min, effective out-diffusion of phosphorus atoms duringepitaxial growth and effective auto-doping are achieved.

According to another embodiment the first dopants include boron atomsand the first semiconductor layer is formed in a deposition chamber at adeposition temperature above 1100° C., at a pressure below 30 Torr (4kPA) and at an HCl flow rate in a range from 0.2 to 1 slm, wherein adeposition rate of at least 1 μm/min, effective out-diffusion of boronatoms during epitaxial growth and effective auto-doping are achieved.

According to another embodiment the first dopants are arsenic atoms, thefirst semiconductor layer is formed at a deposition temperature above1100° C. at a pressure in the deposition chamber of more than 100 Torr(13.3 kPA) or up to atmospheric pressure to achieve a deposition rate ofat least 1 μm/min, effective out-diffusion of arsenic atoms duringepitaxial growth and effective auto-doping are achieved.

According to an embodiment at least one of a deposition temperature, apressure in the deposition chamber and a semiconductor source supplyflow rate can be varied during formation of the first semiconductorlayer to modulate the vertical dopant profile in the first semiconductorlayer.

FIG. 2A illustrates a boron concentration N_(B)(y) in a semiconductorbody versus a distance y to an exposed first surface of thesemiconductor body and shows a simulated vertical dopant profile 901 inthe semiconductor body 100, wherein the semiconductor body 100 includesa homogenously doped substrate portion 120 and a semiconductor layer 190formed by epitaxy on the substrate portion 120. The substrate portion120 has a resistivity of 60 Ohm×cm and contains a homogenous boronconcentration of 2.2×10¹⁴ 1/cm³. The temperature applied during epitaxyis 1135° C., an initial boron contamination is 5×10⁻¹⁴ bar and adeposition rate is 3 μm/min. The simulated vertical dopant profile 901is taken at a thickness of the semiconductor layer of 15 μm.

In the semiconductor layer 190, the simulated dopant profile 901 isexclusively defined by solid-state diffusion and by auto-doping from thesubstrate portion 120. The boron concentration N_(B) (z) falls by twoorders of magnitude across a vertical distance of about 10 μm, wherein asteepness of the simulated vertical dopant profile 901 is less than oneorder of magnitude N_(B) per 4.5 μm. From a comparative dopant profileobtained by a process dominated by solid-state diffusion and with thesame temperature budget applied, the simulated vertical dopant profile901 differs by the less steep decrease.

FIG. 2B schematically shows a vertical dopant profile 903, that gives adopant concentration N(z) in an epitaxially grown semiconductor layer asa function of the distance z to a starting surface for the epitaxyprocess. The semiconductor layer has a vertical extension d2. In a firstregion 904 of the semiconductor layer up to a distance dx from thestarting surface, the vertical dopant profile 903 is dominated bysolid-state diffusion and approximates a Gaussian distribution. In asecond region 905 beyond the distance dx the effect of auto-dopingexceeds the effect of solid-state diffusion and the vertical dopantprofile 903 is significantly less steep than it would be in the absenceof auto-doping.

According to an embodiment the vertical extension d_(y)=d2−d_(x) of thesecond region 905 may be at least two times larger than the first region904. For example, d_(y) is in a range from 2×d_(x) to 5×d_(x).

FIGS. 3A to 3D illustrate a method using accentuated auto-doping byvertical cross-sections through a semiconductor body 100.

FIG. 3A shows a semiconductor body 100, which may be from asingle-crystalline semiconductor material, e.g., Si, Ge, SiGe, SiC, or acompound semiconductor, for example, an A₁₁₁BV compound semiconductorsuch as GaN or GaAs. The semiconductor body 100 may be a flat disk,e.g., a semiconductor wafer, with a planar first surface 101 at a frontside and a planar second surface 102 parallel to the first surface 101at an opposite rear side. A thickness v0 of the semiconductor body 100between the first surface 101 and the second surface 102 may be in arange from 50 μm to 800 μm.

A normal 104 to the first surface 101 defines a vertical direction anddirections parallel to the first surface 101 are horizontal or lateraldirections. The semiconductor body 100 may be low-resistive orhigh-resistive and may be cut from a single-crystalline ingot obtainedby a float zone (FZ) method or a Czochralski (CZ) method, for example,by a Magnetic Czochralski (MCZ) method. Thus, the semiconductor body 100may be a FZ semiconductor body or a CZ semiconductor body such as a MCZsemiconductor body.

A surface portion 110 of the semiconductor body along the first surface101 contains at least a first dose of first dopants. The surface portion110 may be formed by at least one of ion implantation, diffusion fromthe gaseous phase and deposition of a doped layer, wherein ionimplantation may be combined with a heat treatment for bringing theimplanted dopants closer to the first surface.

FIG. 3B shows the surface portion no, which may form a blanket layerdirectly adjoining the first surface 101. A first vertical extension d1of the surface portion 110 may be in a range from 0.02 μm to 2 μm, or ina range from 0.05 μm to 1 μm, by way of example.

An unaffected substrate portion 120 of the semiconductor body 100between the surface portion 110 and the second surface 102 may separatethe surface portion 110 from the second surface 102. In the unaffectedsubstrate portion 120 the portion of the first dopants is less than theportion of the dopants contained in the semiconductor body 100 beforeintroduction of the first dopants.

The first surface 101 forms a starting plane 105 for a semiconductorlayer 190 that is formed by epitaxy on the first surface 101. Thethermal budget applied to the semiconductor body 100 during epitaxy maydiffuse a part of the first dopants also into the direction of thesecond surface 102 such that the surface portion 110 of FIG. 3B expandsat the expense of the unaffected substrate portion 120.

FIG. 3C shows the semiconductor layer 190 that increases the thicknessof the semiconductor body 100, wherein an exposed surface of thesemiconductor layer 190 forms the new first surface 101 of thesemiconductor body 100. A vertical extension d2 of the semiconductorlayer 190 between the first surface 101 and the starting plane 105 maybe in a range from 2 μm to 200 μm, for example in a range from 5 μm to120 μm or in a range from 7 μm to 100 μm. A portion of the semiconductorlayer 190, in which the dopant concentration is dominated by auto-dopingis at least two to five times thicker than a region predominantlydefined by solid-state diffusion.

A vertical extension d12 of the diffused surface portion 111 may begreater than the first vertical extension d1 of the surface portionprior to the formation of the semiconductor layer 190. A dopant dose inthe diffused surface portion 111 may be up to a half of the first dopantdose.

FIG. 3D shows a vertical dopant profile 911 through the semiconductorbody 100 of FIG. 3C along line I-I′ at logarithmic scale, wherein z=0indicates the starting plane 105 of FIG. 3C. For z<0, the dopant profile911 exclusively results from solid-state diffusion of the first dopantsinto direction of the second surface, wherein the dopant profile fallsaccording to a Gaussian distribution. For z>0 the vertical dopantprofile 911 strictly falls from a maximum value at z=0 to a minimumvalue at a significantly lower rate than for z<0.

FIGS. 4A and 4B schematically show a deposition chamber 920 with inlets921, 922 and outlets 923 for process gases. One or more semiconductorbodies 100 are placed in the interior of the deposition chamber 920.

According to FIG. 4A a gaseous dopant source 925 containing a compoundincluding dopant atoms can be fed through a first inlet 921 and agaseous semiconductor source 926 containing a compound includingsemiconductor atoms is fed through a second inlet 922 into thedeposition chamber 920.

During deposition of a semiconductor layer, a control valve 924 may turnoff the supply of the gaseous dopant source 925 as illustrated in FIG.4B over all or part of the deposition process time.

FIGS. 5A to 5D show an embodiment with the vertical dopant profile in anepitaxial grown semiconductor layer 190 shaped by ion implants followedby a heat treatment prior to formation of the semiconductor layer 190.

FIG. 5A shows formation of a surface portion forming a blanket layer ofuniform thickness along a first surface 101 of a semiconductor body 100.An ion beam 108 implants first dopants that settle in the semiconductorbody 100 around an end-of-range peak 114 at a peak distance d11 to thefirst surface 101.

Ion implantation of the first dopants may include one singleimplantation or several implantations at different implantation energiesand/or different implant angles, wherein the implantations result inseveral end-of-range peaks at different distances to the first surface101. An implant angle between the ion beam 108 and the normal 104 ontothe first surface 101 may be at least 7° for avoiding channeling or maybe equal to or less than 7°, e.g., less than 4°, to allow channeling.According to an embodiment ion implantation includes at least onechanneled implant at an implant angle smaller 4° between the ion beam108 and the normal 104.

A heat treatment may diffuse the first dopants, wherein the implantprofile is smoothed and a portion of the implanted ions is diffuseddeeper into the semiconductor body 100.

FIG. 5B shows the surface portion 110 obtained by the heat treatment.The surface portion 110 forms a blanket layer with a first verticalextension d1 along the first surface 101, wherein the first verticalextension d1 of the surface portion 110 is greater than the peakdistance d11.

A semiconductor layer 190 is formed by epitaxy on the first surface 101that forms the starting plane 105 for the epitaxy process.

FIG. 5C shows the semiconductor layer 190 formed between the new firstsurface 101 of the semiconductor body 100 and the starting plane 105 ofthe epitaxial growth.

FIG. 5D shows vertical dopant profiles 931, 932, 933 for thesemiconductor bodies of FIGS. 5A to 5C. The first vertical dopantprofile 931 of the semiconductor body 100 of FIG. 5A shows one singleimplant with an end-of-range peak close to the first surface 101. Thesecond vertical dopant profile 932 of FIG. 5B has a larger spreading andapproximates a Gaussian distribution.

For z<0 the third vertical dopant profile 933 of FIG. 5C represents aGaussian distribution defined by further solid-state diffusion from thesurface portion 110. For z>0 the third vertical dopant profile 933 is toa significant degree less steep than for z<0.

In case of more than one implant at different acceleration energies, thesecond dopant profile 932 may include several peaks that may image intosmooth steps in the third vertical dopant profile 933 between 0<z<d2.

FIGS. 6A to 6C refer to an embodiment introducing the first dose ofdopants and defining the surface portion 110 by deposition of a dopedlayer.

Thickness of a semiconductor body 100 is increased by depositing anin-situ doped layer on the semiconductor body 100, e.g., by epitaxy.

As illustrated in FIG. 6A the in-situ doped layer forms a surfaceportion 110 of the semiconductor body 100 and an exposed surface of thesurface portion 110 forms the first surface 101. Within the surfaceportion 110 the dopant concentration may be approximately uniform. Asemiconductor layer 190 is formed on the first surface 101, wherein thefirst surface 101 serves as starting plane 105 for epitaxy and whereinthe growing semiconductor layer 190 receives doping atoms predominantlyor only by out-diffusion from the surface portion 110.

FIG. 6B shows the semiconductor layer 190 with a vertical extension d2and a diffused surface portion in with a vertical extension d12 greaterthan the first vertical extension d1 of the surface portion of FIG. 6A.

In FIG. 6C a first vertical dopant profile 961 refers to thehomogenously doped surface portion 110 of FIG. 6A and a second verticaldopant profile 692 shows the dopant distribution in the semiconductorbody 100 of FIG. 6B.

The method according to the embodiments may be used to implement dopedstructures and/or doped layers at a rear side of vertical semiconductordevices as illustrated in the following FIGS.

FIGS. 7A to 7D illustrate the formation of a field stop layer based onthe epitaxially grown and auto-doped semiconductor layer 190 of theprevious embodiments.

FIG. 7A shows a semiconductor body 100 including a first semiconductorlayer 190 formed by epitaxy between the first surface 101 and a startingplane 105 for epitaxy, wherein a vertical dopant profile of the firstsemiconductor layer 190 is predominantly defined by auto-doping andwherein a vertical extension d2 of the first semiconductor layer 190 maybe in a range from 5 μm to 35 μm.

A second semiconductor layer 195 is formed on the first surface 101defined by the exposed surface of the first semiconductor layer 190,e.g., by a further epitaxy process including in-situ doping and usingthe exposed surface of the first semiconductor layer 190 as secondstarting plane 106. A vertical extension d3 of the second semiconductorlayer 195 between the new first surface 101 and the second startingplane 106 may be at least 35 μm, for example at least 50 μm or at least100 μm.

FIG. 7B shows the second semiconductor layer 195 formed directly on thefirst semiconductor layer 190. A mean dopant concentration in the secondsemiconductor layer 195 may be lower than a minimum dopant concentrationin the first semiconductor layer 190. The first and second semiconductorlayers 190, 195 may have the same conductivity type.

An anode zone or transistor cells TC may be formed on the first surface101 of the semiconductor body 100, wherein the first surface 101 isformed by an exposed surface of the second semiconductor layer 195.Formation of the transistor cells TC may include further epitaxyprocesses, implant processes, high-temperature annealing steps andfurther patterning processes. A heavily doped contact layer 180 may beformed at the rear side. Formation of the contact layer 180 may include,e.g., a further implant process at the rear side after thinning thesemiconductor body 100 from the rear side, wherein the thinning mayremove at least partly a diffused surface portion as described above. Arear side electrode 320 may be formed that directly adjoins the contactlayer 180. The semiconductor layer 190 is effective as field stop layer.

FIG. 7C schematically shows transistor cells TC formed along a frontside of the semiconductor body 100. The transistor cells TC may bebipolar transistor cells, field effect transistor cells or junctionfield effect transistor cells. The transistor cells TC may beelectrically arranged in parallel and may include planar controlelectrodes, i.e., base electrodes or gate electrodes, or trench controlelectrodes. The first semiconductor layer 190 is effective as field stoplayer and the second semiconductor layer 195 forms a drift zone.

FIG. 7D shows a vertical dopant profile 971 through the first and secondsemiconductor layers 190, 195 along line I-I′ indicated in FIG. 7C. Amean dopant concentration in the second semiconductor layer 195 may belower than a mean dopant concentration in the first semiconductor layer190. A total dopant dose between z=0 and z=d2 can be precisely definedby ion implantation. The enhanced auto-doping in the first semiconductorlayer 190 results in a comparatively smooth transition of the dopantprofile 971 from the field stop layer to the drift zone. In addition,the dopant profile is highly reproducibly.

According to the embodiment illustrated in FIGS. 8A to 8D asemiconductor layer 190 with a vertical dopant profile mainly shaped byauto-doping and with a total dopant content defined by ion implantationforms a drift layer that includes a super-junction structure.

First and second dopants of complementary conductivity type areintroduced into the semiconductor body 100 through a first surface 101,e.g., by ion implantation.

FIG. 8A shows a surface portion 110 including both donors and acceptors,wherein the surface portion 110 may form a blanket layer directlyadjoining the first surface 101. A vertical distribution of the donorsmay differ from a vertical distribution of the acceptors and may beadjusted to compensate for different behavior in the following epitaxyprocess.

A first semiconductor layer 190 with a vertical extension d2 of at least5 μm, e.g., at least 20 μm or even at least 50 μm is formed according tothe above described embodiments, wherein both donors and acceptors arereleased from the surface portion 110 and re-incorporated into the firstsemiconductor layer 190. Trenches 170 are formed in the semiconductorlayer 190.

FIG. 8B shows the trenches 170 extending from the first surface 101 intothe first semiconductor layer 190. The trenches 170 may form a regularpattern of equally spaced long trenches having the same lateral andvertical dimensions and a uniform center-to-center distance p1. Mesaportions 175 of the first semiconductor layer 190 separate neighboringtrenches 170.

A deposition process fills the trenches 170 with high-resistivesemiconductor material. A heat treatment laterally diffuses the donorsand acceptors from the mesa portions 175 into the high-resistivesemiconductor material that fills the trenches 170. Due to differentdiffusion constants, the donors and acceptors diffuse at differentvelocities such that donors and acceptors laterally separate to somedegree. For example, fast diffusing acceptor atoms may form p-typecolumns 182 centered to center axes of the filled trenches 170 and slowdiffusing donor atoms may form n-type columns 181 centered to centeraxes of the mesa portions 175. A center-to-center distance betweenneighboring p-type columns 182 is equal to the center-to-center distancep1 of the trenches of FIG. 8B.

In FIG. 8D the lateral donor profile 981 and the lateral acceptorprofile 982 along line III-III′ in FIG. 8B coincide and indicate auniform distribution of acceptor and donor atoms in the mesa portions175. The higher diffusion velocity of acceptor atoms result in that thelateral donor profile 983 and the lateral acceptor profile 984 alongline IV-IV′ in FIG. 8C differ as regards their spreading.

The vertical donor and acceptor profiles may decrease with decreasingdistance to the first surface 101 at approximately the same rate, sincethe vertical distribution predominantly results from auto-doping insteadof solid-state diffusion and since the vertical distribution of donorsand acceptors in the surface portion 110 of FIG. 8A may be shaped in anappropriate way.

In the auto-doped first semiconductor layer 190 the vertical homogeneityof the compensation degree of the n-type columns and p-type columns ishigh. In addition the total amount of both acceptors and donors can beprecisely defined such that a superjunction structure formed by then-type columns 181 and p-type columns 182 can be formed at narrowtolerance windows.

FIGS. 9A to 9C show the formation of a patterned surface portion 110. Animplant mask layer is deposited on the first surface 101 and patternedby photolithography to form an implant mask 410 covering second portionsof the first surface 101 and including mask openings 415 exposing firstportions of the first surface 101. The mask openings 415 may form aregular pattern with a center-to-center distance p2 between neighboringmask openings 415.

FIG. 9A shows an ion beam 108 that introduce first dopants through themask openings 415 to form a surface portion 110 selectively along thefirst portions of the first surface 101, wherein the surface portion 110has a vertical extension d1. After removal of the implant mask 410 asemiconductor layer 190 is formed by epitaxy on the first surface 101.

FIG. 9B illustrates the semiconductor layer 190, wherein both lateraland vertical distribution of the dopants in the semiconductor layer 190can be precisely defined and reproduced at high uniformity.

In FIG. 9C a lateral dopant profile 991 shows a sequence of maxima at acenter-to-center distance given by the center-to-center distance p2 ofthe mask openings 415 illustrated in FIG. 9A.

FIG. 10 illustrates a vertical phosphorus distribution 995 in asemiconductor layer 190 obtained according to the above describedembodiments. A semiconductor body includes a concentration of 1×10¹⁵1/cm³ boron atoms. An implant at an ion acceleration energy of 80 keVintroduces phosphorus atoms into a thin surface portion along a firstsurface of the semiconductor body. The implanted phosphorus dose is1×10¹³1/cm². A semiconductor layer 190 is formed on the first surface,wherein the temperature applied during epitaxy is 1100° C. and adeposition rate is 3 μm/min.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method for manufacturing semiconductor device,comprising: i) introducing a first dose of first dopants into asemiconductor body having a first surface; ii) increasing a thickness ofthe semiconductor body by forming a first semiconductor layer on thefirst surface of the semiconductor body, and, while forming the firstsemiconductor layer, predominantly setting a final dose of doping in thefirst semiconductor layer by introducing at least 20% of the firstdopants from the semiconductor body into at least a part of the firstsemiconductor layer.
 2. The method of claim 1, wherein the first dopantsare predominantly introduced into the first semiconductor layer byauto-doping.
 3. The method of claim 1, wherein a doping gas supply intoa deposition chamber used for forming the first semiconductor layer isturned off while forming the first semiconductor layer.
 4. The method ofclaim 1, wherein the first dopants are introduced into the semiconductorbody by an ion implantation process.
 5. The method of claim 4, furthercomprising: a diffusion process configured to diffuse the first dopantsdeeper into the semiconductor body.
 6. The method of claim 1, whereinthe first dopants are introduced into the semiconductor body by adiffusion process.
 7. The method of claim 1, wherein a thickness of thefirst semiconductor layer is set in a range from 2 μm to 200 μm.
 8. Themethod of claim 1, further comprising: after carrying out ii),increasing a thickness of the semiconductor body by forming a secondsemiconductor layer on the first surface of the semiconductor body, andsetting an average doping concentration in the second semiconductorlayer smaller than a minimum average doping concentration in the firstsemiconductor layer.
 9. The method of claim 1, wherein the firstsemiconductor layer is formed by chemical vapor deposition or anotherepitaxial deposition in a deposition chamber.
 10. The method of claim 9,wherein the first dopants are phosphorus dopants, the firstsemiconductor layer is formed at a deposition temperature greater than1100° C., at a pressure in the deposition chamber of lower than 30 Torr,and at a H₂ flow rate of smaller than 30 slm.
 11. The method of claim 9,wherein the first semiconductor layer is a silicon carbide layer formedon a silicon carbide substrate and the first dopants are nitrogen orphosphorus dopants, the first semiconductor layer is formed at adeposition temperature greater than 1100° C.
 12. The method of claim 9,wherein the first dopants are boron dopants, the first semiconductorlayer is formed at a deposition temperature greater than 1100° C., at apressure in the deposition chamber of lower than 30 Torr, and at a HClflow rate between 0.2 slm to 1 slm.
 13. The method of claim 9, whereinthe first dopants include arsenic dopants, the first semiconductor layeris formed at a deposition temperature greater than 1100° C., at apressure in the deposition chamber of larger than 100 Torr, and at a H2flow rate of smaller than 30 slm.
 14. The method of claim 13, whereinthe first dopants further include one of phosphorus atoms and antimonyatoms.
 15. The method of claim 9, wherein at least one process parameterof a deposition temperature, a pressure in the deposition chamber, and adeposition rate is varied during formation of the first semiconductorlayer.
 16. The method of claim 1, wherein the first semiconductor layerforms a field stop zone or a buffer zone of an insulated gate bipolartransistor or of a diode or of a power MOSFET.
 17. The method of claim1, further comprising: before carrying out ii), introducing a seconddose of second dopants into the semiconductor body through the firstsurface, the second dopants being of opposite conductivity type than thesecond dopants.
 18. The method of claim 1, wherein the first dopants areintroduced through mask openings of an implant mask on the firstsurface.
 19. The method of claim 1, further comprising: repeating i) andii) with a second dose of second dopants smaller than the first dose offirst dopants.
 20. The method of claim 1, further comprising: before orwhile carrying out i), increasing a thickness of the semiconductor bodyfrom the first surface by forming a doped layer on the semiconductorbody.
 21. The method of claim 1, further comprising: finalizing avertical semiconductor device in the semiconductor body includingforming a first load electrode and a control electrode at the firstsurface of the semiconductor body, and forming a second load electrodeat a second surface of the semiconductor body opposite to the firstsurface.
 22. The method of claim 1, wherein at least 50% of the firstdopants are introduced from the semiconductor body into the firstsemiconductor layer.
 23. The method of claim 1, wherein the firstdopants include atoms of at least two different elements.